TChigini review - Add documentation to the README

The descriptions both in the README file and in the notebooks, require more explanation on the methodology and the results. For example, what is WaterWatch? What is Geospatial Data Assembly? What is the importance of comparing WW with GDA? What is hyswap and its applications. A brief big picture discussion can help the reader understand the motivation behind the work.

More importantly, a discussion on the possible sources of discrepancies between results obtained from WW and GDA.

This issue is to address the suggestions proposed by @cheginit regarding documentation for hyswap-gda on our README.